#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>

using namespace std;

int f(int n)
{
	if (n == 1)
	{
		return 1;
	}
	else if (n == 2)
	{
		return 2;
	}
	else
	{
		return f(n - 1) + f(n - 2);
	}
}

int main()
{
	int n;
	cin >> n;
	int ret = f(n);
	cout << ret;
	return 0;
}